Obesity facts and fiction — can you spot the difference?

If you thought that small changes lead to big weight-loss results, snacking leads to weight gain, or having sex will burn the calories from the huge piece of pie you just ate, you may need to think again.

Obesity researchers reviewed the science behind some popular beliefs about obesity and found that many of these ideas are untrue or unproven. In their report, published in the New England Journal of Medicine, the authors identified seven myths, six presumptions and nine facts about obesity that are pervasive in the press and social media, as well as the scientific literature. The authors' reasoning is included below. Additional comments from Barbara Moore, PhD, CEO of Shape Up America!™ (SUA) are provided in parentheses.


The evidence does not support these seven claims:

  1. Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.

    This is based on an old rule that a person needs to cut out 3500 calories to lose one pound and consume 3500 extra calories to gain one pound. But recent studies show that energy needs change as body mass changes, so if a person has lost weight, cutting out 3500 calories results in smaller changes in weight. The authors explain that the 3500-calorie rule predicts that a person who burns 100 extra calories by walking 1 mile a day will lose more than 50 pounds in 5 years; the actual weight loss is only about 10 pounds.

    (SUA says: Taking small steps to reduce calories is fine, but it doesn't have the same effect over time. As you lose more weight, you need to exercise more and eat fewer calories to keep the weight off. However, making big changes or many changes all at once can be overwhelming. If that's a concern, we recommend taking one step at a time to keep you in your comfort zone and help you stay on track.)

  2. Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.

    While this seems reasonable, several studies have shown that more ambitious goals may help some people lose more weight.

    (SUA says: Many people do well with realistic goals, but some do better with more aggressive goals. When people choose a goal weight, we encourage them to think about why they selected this particular goal and if they ever weighed that as an adult.)

  3. Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.

    A review of weight-loss trials found that rapid weight loss using very-low-calorie diets (less than 800 calories) led to more weight loss than low-calorie diets (800-1200 calories) after 6 months, and there was no significant difference in weight loss between the very-low-calorie and the low- calorie diets in long-term studies that followed up dieters for at least a year.

    (SUA says: Diets that are fewer than 800 calories are restrictive and hard to stick to over time. Studies that follow up at 2 years would be a better indication of long-term results.)

  4. It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.

    Knowing the dieters' stage of change or degree of readiness doesn't predict weight loss or how well they are going to follow the program. However, this may be because people who voluntarily sign up for a weight-loss program are at least somewhat ready to make changes to lose weight.

    (SUA says: We agree that people can sometimes skip a stage and, for example, go from the pre-contemplation stage (not even considering changing) directly to the active weight-loss stage (skipping over considering changing and preparing to change). The important thing is to offer support and guidance that is appropriate to the individual's current stage in the change process.)

  5. Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.

    Physical education, as currently provided in schools, has not been shown to prevent or reduce obesity.

    (SUA says: We agree. Because of budgetary constraints in many schools, gym classes are too often taught by instructors who are not trained and certified as physical education instructors. PE courses in schools are not required daily as they were 30 years ago, nor are they long enough or intense enough to make a sizable difference in rates of obesity. But there are published studies of daily after-school programs that offer vigorous activity, as well as nutrition education, and have been shown to effectively produce weight loss.)

  6. Breast-feeding is protective against obesity.

    The authors state that a World Health Organization (WHO) report that says breast-fed infants are less likely to be obese later in life was flawed and other studies with children did not find strong evidence that breast-feeding prevents obesity. However, breast feeding is encouraged because it offers health benefits for the infant and mother.

    (SUA says: We agree the breastfeeding literature is very disappointing because studies rarely distinguish between EXCLUSIVE breastfeeding and the common practice of mixing breastfeeding with formula feeding and the early use of supplemental cereals and other foods.

    In fact, women rarely breastfeed exclusively for 6 months, but there is evidence that this practice may be protective against childhood obesity. That does not mean the protective effect of exclusive breastfeeding can withstand weaning the infant onto inappropriate foods such as French fries, soda, hot dogs and fried chicken nuggets. Sadly, the Feeding Infants and Toddlers study has shown that this is a common occurrence in contemporary society.)

  7. A bout of sexual activity burns 100 to 300 kcal for each participant.

    A man having intense sexual activity and who weighs 154 lb would burn about 3.5 calories per minute. Since this activity lasts about 6 minutes on average, totaling 21 calories, and about 7 calories are burned just lying down watching TV, the grand total of calories burned during sex is about 14.

    (SUA says: We have long argued that ANY activity counts, but we agree that if you want to burn a significant number of calories, you'll need to find a longer-lasting activity.)


These five statements have not been proven or disproven at the present time.

  1. Regularly eating (versus skipping) breakfast is protective against obesity.

    Two trials found no effect on weight.

    (SUA says: For most people, eating breakfast is a good idea. The National Weight Control Registry, which tracks thousands of adults who have maintained at least a 30-pound weight loss for one year or longer, has found that over three-quarters of successful maintainers eat breakfast every day. Furthermore, in teens, national survey data show an association between skipping breakfast and obesity. But we agree that good randomized controlled studies are needed.)

  2. Early childhood is the period in which we learn exercise and eating habits that influence our weight throughout life.

    Genes may play a role in how a person's BMI progresses over time.

    (SUA says: Forming healthy exercise and eating habits early on can help a child maintain these habits later on in life, but we agree more research is needed. The literature shows that exercise is important for preventing weight regain (after weight loss) and is also useful for preventing weight gain. How the willingness to exercise develops over the life course is poorly understood and may well have a genetic component.)

  3. Eating more fruits and vegetables will result in weight loss or less weight gain, regardless of whether any other changes to one's behavior or environment are made.

    Eating fruits and vegetables is healthy, but it needs to be accompanied by eating fewer calories from other foods so it doesn't lead to weight gain.

    (SUA says: Fruits and vegetables are nutritious and contain fiber and water, which can help fill you up. With few exceptions, they are low in fat and calories. If these foods are part of your meals and replace higher-calorie snacks, they can help with weight control.)

  4. Weight cycling (i.e., yo-yo dieting) is associated with increased mortality.

    Some studies have linked weight cycling with increased risk of death, but this is probably related to a person's health status. Animal studies do not support this association.

    (SUA says: We agree that yo-yo dieting is not proven to cause increased mortality. But it is demoralizing and that is not helpful.)

  5. Snacking contributes to weight gain and obesity.

    Evidence does not consistently show that snacking leads to weight gain or obesity.

    (SUA says: It depends on the snack. High-calorie, high-fat and high-sugar snacks eaten frequently and in large amount can contribute to weight gain. Healthy snacks such as fruit, veggies, low-fat yogurt, and a handful of nuts are reasonable snacks to eat as part of a weight- loss plan.)

  6. The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity.

    Studies linking the risk of obesity and the built environment (parks, roads, architecture) have been inconsistent, so no conclusions can be made.

    (SUA says: Having safe places to walk and play and facilities that are clean and maintained encourage children and adults to participate in activities that can help them maintain a healthy weight.)


These nine facts are supported by evidence and can be used in forming public policy and making recommendations to help people reach a healthy weight.

  1. Although genetic factors play a large role, heritability is not destiny; calculations show that moderate environmental changes can promote as much weight loss as the most efficacious pharmaceutical agents available.
  2. Diets (i.e., reduced energy intake) very effectively reduce weight, but trying to go on a diet or recommending that someone go on a diet generally does not work well in the long-term.
  3. Regardless of body weight or weight loss, an increased level of exercise increases health.
  4. Physical activity or exercise in a sufficient dose aids in long-term weight maintenance.
  5. Continuation of conditions that promote weight loss promotes maintenance of lower weight.
  6. For overweight children, programs that involve the parents and the home setting promote greater weight loss or maintenance.
  7. Provision of meals and use of meal-replacement products promote greater weight loss.
  8. Some pharmaceutical agents can help patients achieve clinically meaningful weight loss and maintain the reduction as long as the agents continue to be used.
  9. In appropriate patients, bariatric surgery results in long-term weight loss and reductions in the rate of incident diabetes and mortality.

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